An X-ray computed tomography apparatus executes controlled-orbit scanning of starting acquiring projection data by being triggered by the arrival of the X-ray tube at a specific rotational angle. This allows to start acquiring projection data from the same rotational angle if acquisition conditions such as a tube current and a top speed are the same. Under different acquisition conditions, however, the apparatus starts acquiring projection data from different rotational angles.
It is an object to provide an X-ray computed tomography apparatus which can start acquiring projection data from an arbitrary top position or rotational angle.